1. Field of the Invention
The present invention relates to an image forming apparatus for generating a plurality of image patterns.
2. Description of the Prior Art
Among conventional output devices for generating a plurality of different patterns, a conventional output device is known which generates a plurality of patterns in a dot pattern instead of printing the patterns by an element or wheel printer. In this apparatus, character code data supplied from a host computer or the like is converted by a character generator to a character dot pattern corresponding to each character code data, and the character dot pattern is generated. The output device of this type can be exemplified by output devices in non-impact printers such as a thermal printer, wire-dot printer, or a laser beam printer.
In these conventional printers, a character generator often generates different type fonts (character patterns) to print different types of characters having different type fonts. In particular, such a character generator tends to be built into a printer for printing English letters since the number of English letters is small. Furthermore, a ROM or RAM cartridge as a character generator is detachably mounted in an output device through a socket, so that a user will be able to select any type font.
The change in type font is performed in many occasions. A bold type font shown in FIG. 1(b) or an italic type font shown in FIG. 1(c) is frequently used in place of the standard type font shown in FIG. 1(a). The bold type font is expressed by increasing a thickness of a line constituting a character. The italic type font is expressed by inclining the character and is used for an emphasis of a character string. More particularly, a change from the standard type font to another type font is performed such that a type font change command is supplied to a printer and an address of the character generator which is specified by the desired type font is changed.
The following problem occurs in the printing device having the removable character generator and any other conventional printing device. When the number of necessary type fonts is increased, a character generator must be able to generate all the required type fonts. As a result, the circuit of the character generator becomes complicated, and the size thereof is increased.
When a specified type font upon reception of a type font change command is not stored in the removable character generator, or when the specified type font is not preset in a character generator in a printer, no means is provided to change the type font and emphasize the line constituting the character in conventional printing devices. In order to overcome this, the following operations are conventionally performed:
(1) A message representing that the specified type font data is not stored is displayed, and printing is completed.
(2) The type font change command is neglected, and the currently used type font is continuously used.
For these reasons, the type font change as the primary object cannot be performed. In addition to this disadvantage, the character string cannot be emphasized.